The Gram-positive, obligate anaerobe C. acetobutylicum was used for the industrial production of the solvents acetone and butanol for over 60 years in the 20th century. With chemical synthesis of acetone and butanol proving significantly more economic, there are no industrial fermentation plants of C. acetobutylicum operational in the world today (11). However, over the last 20 years the genetics and biochemistry of C. acetobutylicum have been investigated in detail as we try to understand and improve upon the processes that control the production of solvents. Biological sources of organic solvents will become more economical as raw materials become more scarce or expensive and the need for renewable solvent sources increase.
Whereas much is known about the biochemistry of C. acetobutylicum metabolism and the genes and proteins that catalyze these processes, relatively little is known about the genetic control of the expression of these genes. Stage 0 Sporulation Protein A (Spo0A) controls both the onset of solventogenesis and the process of sporulation in C. beijerinckii and C. acetobutylicum (30, 20). In strain SKO1 of C. acetobutylicum, where spo0A is deleted, acetone and butanol production is reduced to 2% and 8% of wild type levels respectively. Furthermore, SKO1 cells fail to sporulate and form extended filaments of conjoined rods (20).
Studies have also shown that there are a considerable number of Bacillus subtilis homologues in C. acetobutylicum including sigma factors and other proteins required for sporulation (32, 28). Although solventogenesis does not occur in B. subtilis, it appears that a cascade of sigma factors and stages similar to those involved in B. subtilis sporulation are present in C. acetobutylicum. 
The control of solventogenesis in C. acetobutylicum is genetically linked to the control of sporulation, as shown by the spo0A studies (30, 20). It has been suggested that solventogenesis and sporulation may be genetically uncoupled at some point during early sporulation (19), although as yet there are no reports of any attempts to do so. If solventogenesis could be genetically separated from sporulation, this would serve as an interesting and important illustration of the complexity of bacterial genetic control. Additionally, it may prove useful in bioengineering solvent producing strains of Clostridium for use in industry. A strain of C. acetobutylicum that underwent solventogenesis without entering sporulation would increase solvent production without inactivation, an ideal situation for large scale continuous fermentations.